1. Field of Invention
The present invention relates to a method of improving characteristics of a thin film transistor (TFT), and particularly to a method of hydrogenating a poly-silicon layer.
2. Related Art
Low temperature poly-silicon (LTPS) technology is used to manufacture a thin film transistor (TFT) display of the new generation. Compared to the conventional amorphous silicon (a-Si) TFT, the LTPS display has a main difference in manufacturing: the LTPS display must have an anneal process where an a-Si thin film is transformed into a poly-silicon layer. With the annealing process, the mobility of carriers of the TFT may be increased up to 200 times. Further, the TFT has the advantages of high response speed, high luminance and high resolution. Therefore, the LPTS technology is considered as an indispensable technology for manufacturing the new-generation TFT display.
For the present, the manufacturing of the LTPS TFT display does not have a satisfactory yield, which is limited by the poor stability of the annealing process with a laser. Since the stability of the energy output of the laser and the manufacturing yield are low, a hydrogenation process must be applied to the succeeding process of the LTPS TFT to improve the yield and achieve mass production of the same. However, the whole process of manufacturing the TFT display is hard to control and needs a lengthy process time. Therefore, the hydrogenation technology is a critical process in improving characteristics of the LTPS TFT display.
So far, many hydrogenation technologies have been introduced. Of the hydrogenation technologies, the solid hydrogenation process and the plasma process are the most frequently used. The solid hydrogenation process is conducted by depositing a hydrogen-rich containing layer, such as a silicon nitride layer containing hydrogen (SiNx:H) onto the poly-silicon layer along with a thermal treatment. The hydrogen atoms diffuse into the poly-silicon layer and occupy some regions that are defects in the poly-silicon layer. The plasma process is undertaken to processing a substrate with a hydrogen-containing plasma where the de-ionized hydrogen from the plasma diffuses into the poly-silicon layer and occupies where it needs to be filled in the poly-silicon layer. However, both of the two-hydrogenation technologies need a long time to complete and thus increase the manufacturing costs of the TFT display.